Moving coil type phonograph pickup cartridge

ABSTRACT

A moving coil type phonograph pickup cartridge consisting of a magnet assembly containing a permanent magnet therein and a stylus assembly detachably mounted on the magnet assembly and including an armature with coils wound thereon. The armature is substantially of a V-shape having two leg portions which are at right angles to each other. The coils are wound on the leg portions. By this construction, a vertical tracking angle of a cantilever arm relative to a record disc can be reduced.

United States Patent [451 July 25, 1972 Cho [54] MOVING COIL TYPE PHONOGRAPH PICKUP CARTRIDGE [72] lnventor: Masanobu Cho, Tokyo, Japan [73] Assignee: Micro Seiki Co., Ltd., Tokyo, Japan [22] Filed: Jan. 4, 1971 211 Appl. No.3 103,438

[52] US. Cl. ..l79/100.4l K [51] Int. Cl ..H04r 9/16 [58] Field ofSearch ..l79/100.41 K, 100.41 D, 100.41 S,

l79/l00.41 Z, 100.41 M; 274/36, 37, 38

[56] References Cited UNITED STATES PATENTS 3,184,555 5/1965 Marshall ..179/100.41 K 2,114,471 4/1938 Keller et al.. .....179/100.41 K 3,299,219 1/1967 Madsen ..l79/100.41 K 3,040,136 6/1962 Grado..... ....179/100.41 K 2,631,857 3/1953 Bauer ..274/37 X 2,432,444 12/1947 Roberts... .....274/37 UX 3,538,266 11/1970 Cho ..179/100.41 K

FOREIGN PATENTS OR APPLICATIONS 1,000,035 8/1965 Great Britain ..l79/ 100.41 K

OTHER PUBLICATIONS Shure V-15 Type 11 Cartridge, High Fidelity Magazine, Feb. 1967, pp. 77- 78.

Primary Examiner-Bernard Konick Assistant Examiner-Raymond F. Cardillo, Jr. Attorney-Waters, Roditi, Schwartz & Nissen [5 7] ABSTRACT tracking angle of a cantilever arm relative to a record disc can be reduced.

2 Claims, 9 Drawing Figures P'ATENTED HLZ 912 V 3 679 843 SHEEI 1 BF 3 FIG. I 2 PRIOR ART PRIOR ART MOVING COIL TYPE PHONOGRAPII PICKUP CARTRIDGE This invention relates to a moving coil type phonograph pickup cartridge, and more particularly to a phonograph pickup cartridge having a substantially V-shaped armature on which moving coils are wound.

In a conventional moving coil type phonograph pickup, a moving coil is wound on a substantially square armature or on a cruciform armature having four projecting parts. The conventional moving coil type phonograph pickup, however has various disadvantages, as will be described later with reference to the accompanying drawings, such as a large vertical tracking angle of a cantilever arm and a small equivalent compliance of a stylus tip due to a large mass of the armature.

It is therefore a general object of the present invention toprovide a novel and useful moving coil type phonograph pickup cartridge which has eliminated the disadvantages in the conventional phonograph pickup.

Another object of the invention is to provide a moving coil type phonograph pickup cartridge which has a vertical tracking angle reduced to a desired small angle.

A further object of the invention is to provide a moving coil type phonograph pickup cartridge in which the mass of armature is small and equivalent compliance of stylus tip is large.

A still further object of the invention is to provide a moving coil type phonograph pickup cartridge in which a great magnetic flux density in a gap in a magnetic circuit passing through the armature can be obtained.

Other objects and features of the invention will become apparent from the description made hereinbelow with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a conventional oscillating P FIG. 2 is a diagrammatic vertically sectional side view of a conventional moving coil type phonograph pickup employing the oscillating part shown in FIG. 1;

FIG. 3 is a perspective view showing one embodiment of an oscillating part which constitutes an essential part of a phonograph pickup cartridge according to the invention;

FIG. 4A is a front view of an armature of the oscillating part shown in FIG. 3;

FIG. 4B is a sectional side view of the armature shown in FIG. 4A taken along a line IVB--IVB;

FIG. 5 is a vertically sectional side view of one embodiment of a phonograph pickup cartridge according to the invention;

FIG. 6 is a perspective bottom view of the phonograph pickup cartridge shown in FIG. 5 illustrating a state in which a stylus assembly is detached from a magnet assembly;

FIG. 7 is a perspective view of the stylus assembly shown in FIG. 6 illustrating a state in which a stylus protection cover is closed; and

FIG. 8 is a perspective view of another embodiment of an oscillating part applicable for a phonograph pickup cartridge according to the invention.

First, a conventional moving coil type phonograph pickup will be described with reference to FIGS. 1 and 2. In FIG. 1, an armature 10 is of a substantially square shape with one of its diagonals being vertically disposed. A cantilever arm 11 carrying a stylus 12 on its foremost end is fixed at its rear end on the center of the armature 10. A coil 13 for right channel signal and a coil 14 for left channel signal are wound on the armature 10 as shown in the figure.

FIG. 2 shows a conventional phonograph pickup using the oscillating part shown in FIG. 1. A pickup body 21 consists of a permanent magnet 15 and yokes 16 and 17 rigidly secured to both ends of the permanent magnet 15. The armature 10 on which the coils l3 and 14 are wound is held between the yokes l6 and 17 with gaps 18a and 18b. The cantilever 11 extends through an aperture 19 formed in the yoke 16.

In the conventional phonograph pickup of the above described construction, the armature 10 has a form which is vertically symmetrical with respect to the fixing point of the cantilever 11. Further, the cantilever 11 extends through the aperture 19 of the yoke 16. Accordingly, it is necessary in this conventional phonograph pickup to prevent the bottoms of the armature 10 and the yoke 16 from contacting a surface of a record disc 20. For this reason, a vertical tracking angle 0 of the cantilever 11 relative to the record disc 20 cannot be made small while the stylus 12 is in contact with the record disc 20. For example, the angle 0 in the conventional phonograph pickup of the aforementioned construction is approximately 30. Consequently, this conventional pickup cannot satisfy a requirement for reducing the vertical tracking angle to 15 which is being worldly standardized.

If it is attempted to reduce the angle 0 to, for example, 15, the cantilever 11 must be made longer. By having a sufficiently long cantilever, the angle 0 can be set at a small angle without the bottoms of the armature 10 and the yoke 16 contacting the record disc 20. In this case, however, the long cantilever 11 causes diminishing of output power. This diminishing of output is a considerable disadvantage in the moving coil type phonograph pickup which inherently and essentially has a small output.

It will also be apparent that the aforementioned armature 10 has a large mass due to its shape. Accordingly, an equivalent compliance of the stylus tip in this conventional pickup is small. Furthermore, a large area of the armature 10 necessitates a large cross sectional area of the gaps 18a and 18b between the yokes 16 and 17 in the magnetic circuit. In addition, a magnetic reluctance in the magnetic circuit passing through the yoke 16 is made greater by existing of the aperture 19 in the yoke 16 for the cantilever 11 extending therethrough. Accordingly, a magnetic flux density in the gaps 18a and 18b cannot be made great.

There has been proposed a phonograph pickup using a cruciform armature which has four projecting parts instead of using a square armature. This type of armature, however, has the same disadvantages as described hereinabove.

This invention has eliminated the disadvantages in the aforementioned conventional phonograph pickup. A construction of a phonograph pickup cartridge according to the invention will be described hereinbelow with reference to FIG. 3 and the subsequent figures.

FIG. 3 shows one embodiment of an oscillating part which constitutes an essential part of a phonograph pickup cartridge according to this invention. In FIG. 3, an armature 30 consists of a circular portion 31 and two leg portions 32 and 33 integrally projecting obliquely and upwardly therefrom. The circular portion 31 is formed at its center with an inclined aperture 34.

The leg portions 32 and 33 are so formed that their virtual center lines pass through the center of the aperture 34 and they are at right angles to each other. Accordingly, the leg portions 32 and 33 substantially form a V-shape. A coil 35 for right channel signal and a coil 36 for left channel signal are respectively wound by 40 turns on the leg portions 32 and 33. A cantilever arm 37 carrying a stylus 38 at its foremost end is fitted at its rear end in the aperture 34 of the armature 30 and rigidly secured thereto with epoxy resin.

Nextly, one embodiment of a phonograph pickup cartridge according to the invention incorporating the oscillating part of the above described construction will be illustrated. FIG. 5 shows the vertically sectioned side elevation of the phonograph pickup cartridge and FIG. 6 shows the perspective view of the phonograph pickup cartridge in a state in which its stylus assembly is detached from its magnet assembly.

A phonograph pickup cartridge 50 consists of a magnet assembly 51 and a stylus assembly 52 which is detachably mounted on the magnet assembly 51. A terminal pin holder 53 of the magnet assembly 51 carries a row of projecting pins 54a-57 on one side thereof and another row of projecting pins 54a-57b on the other side thereof. The pins 54b-57b are to be inserted into a pickup arm (not shown). A permanent magnet 58 is housed in a housing 59 of the magnet assembly 51 with an end surface 58a of the N pole and an end surface 581) of the S pole thereof. The end surfaces 580 and 58b are exposed on a surface 60 of the housing 59. An engaging recess 61 is formed on the surface 60 of the housing 59. On both sides of the housing 59, there are provided securing portions 62 and 63 for securing the assembly 51 to the pickup arm by means of screws.

The stylus assembly 52 has its oscillating part in a housing 64 with the cantilever 37 and the stylus 38 projecting through the housing. The assembly 52 has pin receivers 65 at is rear end for receiving the pins 5441-5411. The pin receivers 65 are respectively disposed at positions corresponding to the pins 54a-57.

The armature 30 of the aforementioned oscillating part is secured at its rear surface to one end of a damper 66 made of rubber for damping purpose. The other end of the damper 66 is secured to the front end surface of a yoke 67. The: armature 30 is held in a gap 69 formed between the yokes 67 and 68.

The housing 64 has a protruding portion 70. In FIG. 6, the housing 64 can be carried toward and over the housing 59 by knobs 71 and 72 provided on both sides of the housing 64. By this operation, the pin receiving portion 65 is fitted completely with the pins 54a-1579 and the protruding portion 70 engages the recess 61 of the housing 59 whereby the housing 64 is attached to the housing 59. At this time, upper end surfaces of the yokes 67 and 68 are in contact with the end surfaces 58a and 58b of both poles of the magnet 58. Accordingly, a magnetic circuit passing through the magnet 58, yoke 68, gap 69 and yoke 67 is formed. The direction of the magnetic flux is determined by selection of polarity of the end surfaces 580 and 58b of the magnet 58.

A shield plate 73 is formed with an aperture 74 through which the cantilever 37 projects. Other part of the shield plate 73 shields the yokes 67 and 68 and armature 30 etc. Each two lead wires which are respectively taken out of the coils 32 and 33 wound on the armature 30 extend along the yoke 67 and are connected respectively to two of the four pin receivers 65.

A stylus protection cover 75 which is provided on the housing 64 is pivotable about an axis 76. When the stylus 38 is used, the cover 75 is rotated into a position accommodated in the recess of the housing 64 as shown in FIGS. and 6. When the stylus 38 is not used, as shown in FIG. 7, the cover 75 is rotated into a position in which it covers the cantilever 37 and the stylus 38 projecting through the housing 64. The cantilever 37 and the stylus 38 are protected by the cover 75 and no damage is caused even if the pickup cartridge is erroneously dropped.

In the pickup cartridge of the above described construction, the armature 30 of the oscillating part is constructed as described hereinabove with reference to FIG. 3. Accordingly, the portion of the armature 30 below the fixing point of the cantilever 37 is so small that is does not restict the selection of the vertical tracking angle of the cantilever 37.

Again, the coil winding portions of the armature 30 (namely, the leg portions 32 and 33) are located above the fixing point of the cantilever 37 and, accordingly, it will be sufficient if the lower end of the yoke 68 extends to the position as shown in FIG. 5. The cantilever 37 extends under the lower end of the yoke 68. Therefore, it is not necessary to form an aperture for the cantilever passing therethrough in the yoke 68. As a result, magnetic reluctance in the yoke 68 is small.

Further, since the area of the front surface of the armature 30 is small, the cross sectional area of the gap 69 in which the armature 30 exists may be also small. Due to this small cross sectional area and the small magnetic reluctance, the density of the magnetic flux passing through the gap 69 is great. Again, since the armature 30 is small, its mass is also small and the equivalent compliance of the stylus tip is large.

It is also to be noted that, as described hereinabove, the vertical tracking angle can be reduced while maintaining the same length of the cantilever. If a slight increase in this small vertical tracking angle is allowed, the length of the cantilever can be made shorter than the cantilever of the conventional type of pickup whereby the output power can be increased.

Furthermore, in the conventional pickup, a change of stylus revgfluires a change of whole pickup, whereas, in the picku cartn ge according to the invention of the above describe construction a change of stylus is effected by detaching the stylus assembly 52 from the magnet assembly 51 and changing the stylus assembly only. The magnet assembly 51, having no part that is likely to wear or get out of order, will stand long use.

Nextly, another embodiment of the oscillating part according to the invention will be illustrated with reference to FIG. 8. In FIG. 3 and FIG. 8, like reference numerals designate like parts and the description thereof will be omitted. An armature consists of two leg portions 81 and 82 which substantially form a V-shape. A cantilever 37 is secured rigidly on a root portion 83 at a crossing point of virtual center lines of both leg portions 81 and 82. The leg portions 81 and 82 are at right angles with each other and have the coils 35 and 36 wound thereon. If this embodiment of oscillating part is employed in the phonograph pickup cartridge the same features and advantages as described hereinabove will be obtained.

While the present invention has been described with reference to a few particular embodiments, it is to be understood that these embodiments are only for illustrative purpose and the present invention may have various modifications and changes without departing from the spirit and the scope of the invention as defined by the appended claims.

What I claim is:

1. A moving coil type phonograph pickup cartridge comprising:

a stylus assembly comprising;

a cantilever arm, a stylus provided at the foremost end of said cantilever arm, an armature having two leg portions which extend obliquely and upwardly with a right angle to each other, said armature being provided with the rear end of said cantilever arm which is secured to a crossing point of virtual center lines of said two leg portions, coils wound around respective of said two leg portions, two yoke member located so as to form an air gap between the opposed end surfaces thereof, a damping member attached of its both surfaces to the rear surface of said armature and to the end surface of one of said yoke members so that the leg portions of said armature are located in said air gap formed between the yoke members, a housing for accommodating said yoke members, said damping member and said armature, said cantilever arm extending through said housing and substantially extending of its virtual axis through said armature, said damping member and a part of said one yoke member, and terminals provided at the housing and electrically connected to said coils;

a magnet assembly comprising;

a housing, a permanent magnet accommodated in said housing and exposing the magnetic poles thereof at the lower surface, and terminals provided in said housing for being connected with the terminals of said stylus assembly and with terminals of a pickup arm, said permanent magnet being positioned in the housing so that the permanent magnet forms a magnetic circuit in said yoke members passing through said air gap when the stylus assembly is connected to the magnet assembly by connecting of the terminals of the stylus assembly with the terminals of the magnet assembly.

2. The moving coil type phonograph pickup cartridge as defined in claim 1, in which said armature comprises a circular portion at the center of which said rear end of the cantilever arm is secured and said two leg portions projecting from the upper portion of the circular portion, said circular portion having the circular lower portion with no projection.

i l I! I! i 

1. A moving coil type phonograph pickup cartridge comprising: a stylus assembly comprising; a cantilever arm, a stylus provided at the foremost end of said cantilever arm, an armature having two leg portions which extend obliquely and upwardly with a right angle to each other, said armature being provided with the rear end of said cantilever arm which is secured to a crossing point of virtual center lines of said two leg portions, coils Wound around respective of said two leg portions, two yoke member located so as to form an air gap between the opposed end surfaces thereof, a damping member attached of its both surfaces to the rear surface of said armature and to the end surface of one of said yoke members so that the leg portions of said armature are located in said air gap formed between the yoke members, a housing for accommodating said yoke members, said damping member and said armature, said cantilever arm extending through said housing and substantially extending of its virtual axis through said armature, said damping member and a part of said one yoke member, and terminals provided at the housing and electrically connected to said coils; a magnet assembly comprising; a housing, a permanent magnet accommodated in said housing and exposing the magnetic poles thereof at the lower surface, and terminals provided in said housing for being connected with the terminals of said stylus assembly and with terminals of a pickup arm, said permanent magnet being positioned in the housing so that the permanent magnet forms a magnetic circuit in said yoke members passing through said air gap when the stylus assembly is connected to the magnet assembly by connecting of the terminals of the stylus assembly with the terminals of the magnet assembly.
 2. The moving coil type phonograph pickup cartridge as defined in claim 1, in which said armature comprises a circular portion at the center of which said rear end of the cantilever arm is secured and said two leg portions projecting from the upper portion of the circular portion, said circular portion having the circular lower portion with no projection. 